crypto/scheduler: fix multicore rings re-use

crypto/scheduler: fix multicore rings re-use

When scheduler mode changed from multicore to roundrobin and
back to multicore, scheduler tries to create memory rings with
the same name and fails. The fix allows to lookup and re-use
previously allocated memory rings.

Fixes: 4c07e0552f0a ("crypto/scheduler: add multicore scheduling mode")
Cc: stable@dpdk.org
Signed-off-by: Kirill Rybalchenko <kirill.rybalchenko@intel.com>
Acked-by: Pablo de Lara <pablo.de.lara.guarch@intel.com>
Acked-by: Fan Zhang <roy.fan.zhang@intel.com>
Tested-by: Reshma Pattan <reshma.pattan@intel.com>